The invention relates to the genetic manipulation of plants, particularly to transforming plants with genes that regulate cell cycle, cell proliferation and enhance disease resistance.
Prohibitin is an intracellular protein of about 280 amino acids. The protein was first discovered in mammalian cells during studies of cell senescence. The mammalian gene has been cloned and is associated with antiproliferative activity based on the capacity of microinjected prohibitin mRNA to inhibit cell cycle progression in human diploid fibroblasts.
The rat prohibitin gene was isolated for its ability to negatively regulate cell proliferation. The gene was isolated from mRNAs that were more frequently expressed in normal liver than in regenerating liver and thus was considered as a candidate for one of the tumor suppressor genes associated with breast and ovarian cancer. Prohibitin was also found to share substantial homology with the product of the Drosophila Cc gene, which encodes a protein of unknown function required for the larval to pupal transition in the fruit fly. Prohibitins are also implicated in controlling senescence and aging, with which there may be a functional link to their antiproliferative function and cell cycle control.
The prohibitin gene appears to be evolutionarily conserved. The 30 kD protein has been associated with antiproliferative activity based on the capacity of microinjected prohibitin mRNA to inhibit cell cycle progression in human diploid fibroblast-like cells. A role has been suggested for prohibitin in cell cycle regulation, replicative senescence, cellular immortalization, and the development of sporadic breast tumors. The gene is expressed in a wide variety of tissues and organisms. Prohibitin has been identified as a gene that is expressed in resting but not in dividing cells.
Disease in plants is caused by biotic and abiotic causes. Biotic causes include fungi, viruses, bacteria, and nematodes. Of these, fungi are the most frequent causative agent of disease on plants. Abiotic causes of disease in plants include extremes of temperature, water, oxygen, soil pH, plus nutrient-element deficiencies and imbalances, excess heavy metals, and air pollution.
A host of cellular processes enables plants to defend themselves from disease caused by pathogenic agents. These processes apparently form an integrated set of resistance mechanisms that is activated by initial infection and then limits further spread of the invading pathogenic microorganism.
As noted, among the causative agents of infectious disease of crop plants, the phytopathogenic fungi play the dominant role. Phytopathogenic fungi cause devastating epidemics, as well as causing significant annual crop yield losses. All of the approximately 300,000 species of flowering plants are attacked by pathogenic fungi. However, a single plant species can be host to only a few fungal species, and similarly, most fungi usually have a limited host range.
Plant disease outbreaks have resulted in catastrophic crop failures that have triggered famines and caused major social change. Generally, the best strategy for plant disease control is to use resistant cultivars selected or developed by plant breeders for this purpose. However, the potential for serious crop disease epidemics persists today, as evidenced by outbreaks of the Victoria blight of oats and southern corn leaf blight. Accordingly, molecular methods are needed to supplement traditional breeding methods to protect plants from pathogen attack. Additionally, methods are needed to control cell division and proliferation in plants.
Compositions and methods for altering cell cycle processes and cell proliferation are provided. The compositions comprise plant nucleotide sequences and proteins useful for manipulation, differentiation, development and cellular division. The sequences find use in methods for the manipulation of cell growth, both positively and negatively.
In one embodiment, the nucleotide and amino acid sequences of the invention may find use in enhancing plant culture methods and transformation. The sequences may additionally find use in methods for the activation of the plant pathogen defense system. That is, the compositions and methods of the invention can be used for enhancing resistance to plant pests. The method involves stably transforming a plant with a gene capable of inducing the plant pathogen defense system operably linked with a promoter capable of driving expression of a gene in a plant cell.
It is recognized that a variety of promoters will be useful in the invention, the choice of which will depend in part upon the desired level of expression of the disclosed genes. It is recognized that the levels of expression can be controlled to induce the disease resistance pathway resulting in levels of immunity in the plant which impart resistance in the plant to the pathogen or to induce cell death. The methods of the invention find use in controlling plant pests, including fungal pathogens, viruses, nematodes, insects, and the like.
Transformed plants and seeds, as well as methods for making such plants and seeds are additionally provided.